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Phase dependences in the binary system lead chlorapatite Pb10(PO4)6Cl2 — calcium fluorapatite Ca10(PO4)6F2 with special regard to polymorphic transitions of initial compounds have been examined. Phase diagram of this system over the full temperature and composition range has been provided and the occurrence of solid solutions discovered. The investigations have been carried out by the thermal, microscopic, X-ray and dilatometric analyses.

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Study of the mechanism of optical resolutions via diastereoisomeric salt formation

2. Thermoanalytical and X-ray study of solid solution formation during the resolution of racemic malic acid by R-α-phenylethylamine

Journal of Thermal Analysis and Calorimetry
Authors: D. Kozma, Klára Tomor, C. Novák, G. Pokol, and E. Fogassy

Racemic malic acid (I) was resolved by R-α-phenylethylamine(II). The S-(−)-I.R-(+)-II diastereoisomer was in excess in the precipitated salt. DSC curves and X-ray powder diffractograms proved that the diastereoisomeric salt mixture precipitated during the resolution was isomorphous with the optically pure S-(−)-I.R-(+)-II salt. The diastereoisomeric salt mixture containing the R-(−)-I.R-(+)-II salt in abundance bound crystal solvate (water or methanol) when produced by the total evaporation of the mother liquor, while the optically pure R-(−)-I.R-(+)-II salt crystallized without solvate. It is generally assumed that solid solution formation takes place when the two diastereoisomers are alike and the high similarity results in less efficient enantiomer separation.

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Abstract  

The polycrystalline ceramic samples of general formula Pb1−XCaXTiO3 with X = 0.00, 0.1, 0.2 and 0.3 have been synthesized by standard high temperature solid state reaction method using high purity oxide and carbonates. The formation of the single phase compounds have been checked by X-ray diffraction technique. The Modulated Differential Scanning Calorimetry has been used to investigate the effect of substitution on the phase transition temperature and the corresponding change on the enthalpy and other thermal parameters of the substituted compound/solid solutions. It was observed that the phase transition temperature (T c) decreases linearly with the increase of substitution concentration. The linear decrease in T c with increase of substitution concentration may be useful for the eventual functionality of the materials for different ferroelectric devices. The results are discussed in detail.

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Abstract  

The iron bearing phases present in a ferromanganese nodule from the Central Indian Ocean have been determined using57Fe Mössbauer spectroscopy. The Mössbauer results have been corroborated by XRD, IR and TG-DTA studies. The Mössbauer spectrum of a ferromanganese nodule shows a broad line width which indicates the presence of more than one iron bearing paramagnetic oxide or oxyhydroxide phases where iron is present as Fe3+. -FeOOH has been distinctly characterised as one of the iron bearing phases in the nodule. Other oxyhydroxide and oxide phases of iron in the nodule have been ruled out. A typical paramagnetic doublet persists even at very high temperature which has been proposed to be due to iron(III)phosphate. Formation of solid solution of Mn2O3–Fe2O3 has been observed in the heat treated nodule at 1073 K, which has been characterised by the Mössbauer technique.

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Abstract  

Multilayers constituted by very thin films of Fe and Al, deposited by thermal evaporation and magnetron sputtering techniques and then aged in air at temperatures in the 300–400 K range for times up to 200 h, were analyzed by means of XRD, CEMS, XPS and AES measurements. Fe(Al) solid solutions form during evaporation because of interdiffusion phenomena at the Fe–Al interfaces, while Al undergoes oxidation during sputtering deposition and, consequently, the multilayers are constituted by Fe intercalated with Al2O3 films. Aging treatments in oxidizing environments induce no significant modification in sputtered multilayers while, on the contrary, the evaporated multilayers show the effects of both interdiffusion and oxidation phenomena.

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Abstract  

Method for synthesis of UO2+x and uranium–thorium mixed oxides by using sol–gel method and mechanochemical activation is proposed. The synthesis of UO2+x and solid solutions with equal amount of metals or enriched to one of them is performed by external gelation process, thermal decomposition of the sol–gel products in air and subsequent mechanochemical activation in air in stainless steel vessels. The crystal structures of the obtained oxides before and after the mechanochemical treatment are analysed by the use of X-ray diffraction method. Quantitative phase analysis and calculations of the size of the crystallites, lattice parameters, and densities of the oxides are performed by BRASS program for Rietveld calculation. The proposed method leads to decrease of the lattice parameters and thus to higher density of the obtained oxides with crystallites size in the range of 12–16 nm.

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Abstract  

The state diagrams (T-x) of the systems Ag2Te-ZnTe(I) and Ag2Te-Zn(II) are offered on the ground of data obtained by differential thermal analysis, X-ray phase analysis, microstructural analysis and measurements of the density and the microhardness of samples synthesized. The systems studied are quasibinary sections of the ternary system Ag-Zn-Te. System I is characterized by two eutectic and three eutectoidal non-variant equilibria as well as by an intermediate compound Ag2ZnTe2, which melts congruently at 880C. The latter exists in the range from 120 to 880C in two polymorphic modifications (Tʅ→β=515C). System II is characterized by one eutectic, two eutectoidal and one peritectic nonvariant equilibria, boundary solid solutions on the ground of Ag2Te and Zn and one intermediate phase of the composition Ag4Zn3Te2, which melts congruently at 880C.

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Abstract  

By means of differential scanning calorimetry (DSC) the precipitation process from a supersaturated solid solution of Cu−0.65 at% Co−0.33 at% Si (Cu−1 at% Co2Si) was investigated. On the basis of enthalpimetric calculations it was found that the decomposition begins with cobalt precipitation. Clustering of atoms of cobalt initiates the precipitation of silicon, and particles of the stoichiometric Co2Si composition are finally formed. Kinetic parameters were obtained by a convolution method based on the Mehl–Johnson–Avramiformalism. Their values are all in agreement with the experimentally observed behavior displayed by DSC traces. Decay kinetics of cobalt and silicon matrix during simulated isothermal calculations using DSC data reveals good agreement with similar computed results reported in literature. Precipitate dissolution obeys quite well to a three-dimensional diffusion kinetic law previously developed.

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Solid state reactions in the platinum–mercury system

Thermogravimetry and differential scanning calorimetry

Journal of Thermal Analysis and Calorimetry
Authors: G. Souza, I. Pastre, A. Benedetti, C. Ribeiro, and F. Fertonani

Abstract  

Thermogravimetry, Differential Scanning Calorimetry and other analytical techniques (Energy Dispersive X-ray Analysis; Scanning Electron Microscopy; Mapping Surface; X-ray Diffraction; Inductively Coupled Plasma Atomic Emission Spectroscopy and Cold Vapor Generation Atomic Absorption Spectroscopy) have been used to study the reaction of mercury with platinum foils. The results suggest that, when heated, the electrodeposited Hg film reacts with Pt to form intermetallic compounds each having a different stability, indicated by at least three mass loss steps. Intermetallic compounds such as PtHg4, PtHg and PtHg2 were characterized by XRD. These intermetallic compounds were the main products formed on the surface of the samples after partial removal of bulk mercury via thermal desorption. The Pt(Hg) solid solution formation caused great surface instability, attributed to the atomic size factor between Hg and Pt, facilitating the acid solution’s attack to the surface.

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Abstract  

Crystallization, morphology and mechanical properties of a spodumene-diopside glass ceramics with adding different amount of CaO and MgO in Li2O-Al2O3-2SiO2 were investigated. With CaO and MgO addition, the crystallization temperature (T p) decreased, the value of Avrami constant (n) decreased from 3.2±0.3 to 1.4±0.2, the activation energy (E) increased from 299±3 kJ mol−1 to 537±5 kJ mol−1. The crystalline phases precipitated were h-quartz solid solution, β-spodumene and diopside. The mechanism of crystallization of the glass ceramics changed from bulk crystallization to surface crystallization. The grain sizes and thermal expansion coefficients increased while flexural strength and fracture toughness of the glass-ceramics increased first, and then decreased. The mechanical properties were correlated with crystallization and morphology of glass ceramics.

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